The gene inhibits the enzyme calcineurin, which in turn inhibits PKA, another naturally occuring enzyme. PKA enhances the connections between neurones and therefore enables memories to be stored.

In effect, researchers are switching off the brain's natural ability to limit how much information is remembered. "It confirms what is really common sense - that you only want to store important things in memory, so you need inhibitory constraints that you have to overcome," said HHMI researcher and co-author Dr Eric Kandel.

Once these constraints were overcome by making mice calcineurin-inhibited, they performed better than normal mice in memory trials. In one test, the engineered mice were better able to remember when familiar objects were moved to novel locations or replaced with novel objects.

Researchers found that the this boosted memory could also be switched off if the animals were given doxycycline, an antibiotic which counteracted the inhibitory effect of the gene on cacineurin.

"You worry in such experiments that the animals' memory will become better or worse because you've somehow interfered with some normal function during development", said Dr Kandel. "But we found that was not the case; and we also did experiments showing that the animals can see, smell and locomote perfectly well, and are well motivated. So we really are seeing an effect on hippocampal learning."

The calcineurin-inhibited animals also had better spatial memory and could remember better than normal mice the location of a platform in a murky water pool. And, the scientists performed tests showing that working memory (memory of immediate past circumstances) was not affected by the inhibition. In those tests, the animals were required to find food in a radial-arm maze, a task enhanced by immediate recall of the maze arms already explored.

In similar research, two years ago, Princeton University researchers announced they had created a smart mouse which showed remarkable performance in memory tests, even as it aged. Christened Doogie, the mouse was engineered to have extra copies of a gene called NR2B which coded for a receptor protein called NMDA. This receptor forms memories when stimulated by signals arriving from nerves in the brain.